Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Derivative liability statement of financial position not disclosed flag	interest rate derivative instruments
ASSETS
Cash equivalents		$ 10
Commodity contracts, assets	$ 132,229
Commodity contracts assets, other	(21,163)
Nuclear decommissioning trust	1,073,410	1,201,246
Nuclear decommissioning trust, other	476,409	408,849
Other special use fund	347,231	362,781
Other special use funds, other	963	2,196
Total assets	1,552,870	1,570,845
Total assets, other	456,209	409,356
LIABILITIES
Derivative instruments, other	15,357
Derivative instruments, total	(42,446)
Total liabilities	(42,446)
Total liabilities, other	15,357
Commodity contracts
ASSETS
Commodity contracts, assets	132,098	6,808
Commodity contracts assets, other	(21,163)	(1,689)
LIABILITIES
Derivative instruments, other	15,357	4,823
Derivative instruments, total	(41,537)	(123,888)
Interest rate swaps
ASSETS
Commodity contracts, assets	131
Commodity contracts assets, other	0
LIABILITIES
Derivative instruments, other	0
Derivative instruments, total	(909)
Equity securities
ASSETS
Nuclear decommissioning trust	18,485	10,297
Nuclear decommissioning trust, other	3,827	(767)
Other special use fund	67,937	43,187
Other special use funds, other	963	2,196
U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	472,582	409,616
U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	211,923	319,734
Other special use fund	275,267	319,594
Corporate debt
ASSETS
Nuclear decommissioning trust	149,226	188,317
Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	147,938	208,306
Municipal bonds
ASSETS
Nuclear decommissioning trust	64,881	59,323
Other special use fund	4,027	0
Other fixed income
ASSETS
Nuclear decommissioning trust	8,375	5,653
Level 1
ASSETS
Cash equivalents		10
Commodity contracts, assets	0
Nuclear decommissioning trust	226,581	330,798
Other special use fund	342,241	360,585
Total assets	568,822	691,393
LIABILITIES
Derivative instruments	0
Total liabilities	0
Level 1 | Commodity contracts
ASSETS
Commodity contracts, assets	0	0
LIABILITIES
Derivative instruments	0	0
Level 1 | Interest rate swaps
ASSETS
Commodity contracts, assets	0
LIABILITIES
Derivative instruments	0
Level 1 | Equity securities
ASSETS
Nuclear decommissioning trust	14,658	11,064
Other special use fund	66,974	40,991
Level 1 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	0	0
Level 1 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	211,923	319,734
Other special use fund	275,267	319,594
Level 1 | Corporate debt
ASSETS
Nuclear decommissioning trust	0	0
Level 1 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	0	0
Level 1 | Municipal bonds
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 1 | Other fixed income
ASSETS
Nuclear decommissioning trust	0	0
Level 2
ASSETS
Cash equivalents		0
Commodity contracts, assets	127,260
Nuclear decommissioning trust	370,420	461,599
Other special use fund	4,027	0
Total assets	501,707	463,480
LIABILITIES
Derivative instruments	(26,783)
Total liabilities	(26,783)
Level 2 | Commodity contracts
ASSETS
Commodity contracts, assets	127,129	1,881
LIABILITIES
Derivative instruments	(25,874)	(127,016)
Level 2 | Interest rate swaps
ASSETS
Commodity contracts, assets	131
LIABILITIES
Derivative instruments	(909)
Level 2 | Equity securities
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 2 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	0	0
Level 2 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 2 | Corporate debt
ASSETS
Nuclear decommissioning trust	149,226	188,317
Level 2 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	147,938	208,306
Level 2 | Municipal bonds
ASSETS
Nuclear decommissioning trust	64,881	59,323
Other special use fund	4,027	0
Level 2 | Other fixed income
ASSETS
Nuclear decommissioning trust	8,375	5,653
Level 3
ASSETS
Cash equivalents		0
Commodity contracts, assets	26,132
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Total assets	26,132	6,616
LIABILITIES
Derivative instruments	(31,020)
Total liabilities	(31,020)
Level 3 | Commodity contracts
ASSETS
Commodity contracts, assets	26,132	6,616
LIABILITIES
Derivative instruments	(31,020)	(1,695)
Level 3 | Interest rate swaps
ASSETS
Commodity contracts, assets	0
LIABILITIES
Derivative instruments	0
Level 3 | Equity securities
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 3 | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	0	0
Level 3 | U.S. Treasury debt
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 3 | Corporate debt
ASSETS
Nuclear decommissioning trust	0	0
Level 3 | Mortgage-backed securities
ASSETS
Nuclear decommissioning trust	0	0
Level 3 | Municipal bonds
ASSETS
Nuclear decommissioning trust	0	0
Other special use fund	0	0
Level 3 | Other fixed income
ASSETS
Nuclear decommissioning trust	0	0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
ASSETS
Nuclear decommissioning trust	$ 472,582	$ 409,616